Abstract
Hyperventilation is a popular therapy for improving systemic oxygenation in infants with pulmonary hypertension. To determine the effects of hypocapnea on cerebral blood flow velocity and intracranial pressure, we studied 6 infants with severe pulmonary hypertension, GA 38-43 wks, during normocapnea and moderate and extreme hypocapnea. Arterial PCO2, (PaCO2) was altered by changing ventilator rate. Mean airway pressure and arterial PO2 were kept constant by changes in ventilator pressure and inspired oxygen concentration. We measured transfontanel intracranial pressure (ICP) and mean arterial blood pressure (BP). Cerebral blood flow velocity (CBFV) was assessed by Doppler technique. The maximum amplitudes of advancing flow velocity during systole and diastole were measured and the pulsatility index calculated.These findings suggest that extreme hyperventilation significantly reduces advancing cerebral blood flow velocity and may reduce total cerebral blood flow. Therefore, despite an improvement in systemic PO2, cerebral oxygenation may suffer.
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